URI senior assesses Rhode Island’s amphibian populations

Media Contact: Todd McLeish 401-874-7892

KINGSTON, R.I. — November 12, 2002 — For each of the last three summers, University of Rhode Island senior Dan Linden was deep in the thick of wildlife research.

He wallowed in the mud and waded into ponds and wetlands every day seeking frogs and salamanders to assess their populations and determine what factors affect breeding success.
Working in cooperation with URI Associate Professor Peter Paton and graduate student Scott Eagan, the Warwick resident monitored 120 ponds and vernal pools by counting every creature he could find. Using dip nets and minnow traps, he collected and identified each pond’s wildlife, including tadpoles, frogs, salamanders, aquatic insects and other invertebrates.

One factor Linden determined to have an important impact on amphibian populations is the density of roadways surrounding the ponds. “Road density creates barriers for them to cross that will be death zones,” Linden said. “If you’ve got a pond in an area with a lot of woods and roads, where the frogs will be crossing the roads to move from the woods to the pond to breed, high mortality rates will result.”

Many ponds surrounded by roads were also found to be polluted, another reason that amphibian populations were low in those locations. “Sometimes we’d see an oil slick on a pond and know that the oil had either killed the tadpoles directly or the oil killed the plants that the tadpoles feed on. Either way there wasn’t much life to be found,” said the 21-year-old wildlife biology major.

Other factors Linden found to affect amphibian populations include the quantity of woody vegetation in and around ponds and the ponds’ hydrology and hydroperiod – the length of time they hold water.

On a typical day, Linden visited 5 to 10 ponds in the state to assess the abundance of species at each site. “One of the hardest parts of the project was tadpole identification,” he said. “When they’re small, they don’t have distinct features, so it’s very difficult to distinguish between them. For some, the only way to identify them is under a microscope looking at their rows of teeth. After looking at a lot of them, though, we learned to identify them at a glance.”

Among the species he found were wood frogs, green frogs, bullfrogs, pickerel frogs, spring peepers, American toads, marbled salamanders, spotted salamanders, two-lined salamanders, four-toed salamanders and red-spotted newts. In addition he caught giant water bugs, water scorpions, predacious diving beetles and ferocious water bugs. Some of these aquatic insects prey on tadpoles, so their presence can affect tadpole populations.

In addition to his amphibian research, Linden also studied the endangered American burying beetle on Block Island and conducted a census of reptile, amphibian and small mammal species on 12 properties owned by the Weekapaug Foundation for Conservation in Westerly.
Funding for Linden’s research was provided by the URI Agricultural Experiment Station through the URI Coastal Fellows Program, a unique program designed to involve undergraduate students in addressing current environmental problems. Now in its seventh year, the Coastal Fellows Program teams students with faculty, research staff and graduate students to help them gain skills that will ensure their future success.

After he graduates in May, Linden intends to go to graduate school somewhere in the Northeast. “I’d like to eventually get my Ph.D. and become a professor and do research. I’d like to get into studying large mammals.”